Diesel Oxidising Catalyst (DOC)

A diesel oxidation catalyst cleaning (DOC) is a device that breaks down the pollutants from a diesel engine in the exhaust stream by using a chemical process aimed at turning the pollutants into less harmful components. It tends to closely resemble an automobile’s catalyst converter.

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Understanding the Diesel Oxidation Catalyst (DOC)

The DOC is designed to convert carbon monoxide and hydrocarbons into carbon dioxide and water. It essentially breaks down pollutants in the exhaust system from a diesel engine which helps reduce particulate matter.

How it works

The exhaust flows straight through the DOC substrate with very little restriction. In the aftertreatment system, there is a hydrocarbon dosing system where fuel is dosed at a specific temperature; the fuel turns into a vapor and that vapor starts the chemical reaction which produces heat. The ECM has a thermal management system where it maintains that heat and this process allows the diesel particulate filter to operate at peak performance

Can the DOC be cleaned like a Diesel Particulate Filter (DPF)?

Yes, anytime the DPF is removed for cleaning, the DOC should be removed, inspected, and cleaned as well. It is recommended to follow the same cleaning method as the DPF. When technicians see a DPF fault code many times they will focus on cleaning the DPF but leave the DOC in place. This is a mistake because the DOC is a flow-through device. Therefore, what is in the filter has passed through the DOC and it should be cleaned as well. If the DOC is not clear, it can become face plugged and this is part of a bigger problem that needs to be diagnosed.

Why Does a DOC Fail?

DOCs are coated with precious metals and over time these deteriorate causing the DOC to fail. The DOC has no moving parts, resulting in it having a long lifecycle. Therefore 80% of DOC and DPF failures are premature due to engine-related issues.

The DOC has one job, which is to create heat for soot oxidation, but if the engine is not running properly because of bad injectors or a turbo issue, or the aftertreatment system is not operating properly due to exhaust leaks or a leaking hydrocarbon doser, the DOC will fail prematurely. We will see DOC contamination which in turn could poison the DOC and cause DOC face plugging.

What is DOC Face Plugging?

Face plugging is an extreme build-up of carbon on the inlet side of your DOC. This extreme build-up causes additional exhaust backpressure and restricts exhaust flow, which hinders the performance of the DPF and SCR downstream.

Diesel Oxidising Catalyst (DOC) – Cleaning

To keep your DOC’s optimal operating performance, we suggest a clean at least every 12 months in conjunction with your DPF. Shorter timeframes may be needed if your vehicle is exposed to peak hour traffic at low speeds, short stop/start trips or extended periods where engine is at idle.

DOC’s do not become blocked like a DPF does because they aren’t catching particulates but more so are converting carbon monoxide (CO) and hydrocarbons into carbon dioxide (CO2) and water. It may have an accumulation of deposits on the catalyst’s internal construction over time which Australian DPF Centre can remove using our state of the art machines and equipment.